Because of its electrical and heat conducting properties, copper has many important uses in the form of wire, sheet, etc. However, pure copper has relatively weak tensile strength. One promising approach to improving the strength of copper is alloying it with a metal which forms a dendritic phase in the copper matrix. Such multi-phase copper alloy mixtures have been referred to as "in-situ" composites. The alloying metal is present as an array of dendrites.
It has been demonstrated that quite high strength copper-dendritic alloys can be produced by alloying copper with elements such as niobium, vanadium, or iron. See Bevk et al. (1978); and Bevk, et al. (1982). High strength sheets or wires may be fabricated by a casting and mechanical reduction process. The casting is first produced as a microstructure of X dendrites in a Cu matrix, and the alloy is then mechanically reduced by either rolling or drawing operations. This kind of mechanically worked copper composite alloy is described by Downing, et al. (1987), and Verhoeven, et al. U.S. Pat. No. 4,378,330.
Cu-X dendrite type alloys are quite ductile and may be mechanically reduced to very large drawing strains without breakage. Mechanical reduction, such as by drawing, extrusion, or rolling, converts the X dendrites into elongated filaments, which serve to reinforce and greatly increase the strength of the formed wire, sheet, or other configuration.
In the development of this copper-dendrite technology for practical use, a problem has arisen which remains to be resolved. As the reduction in area ratio, A.sub.o /A (where A.sub.o =original area and A =final area) is increased the strength of the alloy is observed to increase. However, wire diameters for the highest strengths are extremely small, such as 25 mm (0.001 inch).
Reduced strengths with larger size ingots for a given A.sub.o /A value result because the dendrite size in the larger ingot is increased. For example, the dendrite size in the 15 gm ingots of Bevk (1982) was about 2 .mu.m compared to 7 .mu.m in the larger ingot. Ultimate tensile strengths correlate approximately with S.sup.-0.5, where S is the spacing of the X filaments produced from the X dendrites in the casting. Consequently, for a given composition of the X component, the dendrite spacing will inherently increase as the casting size increases because of the reduced solidification rates required with the lower surface to volume ratio of larger sized ingots. For scale up to larger sized ingots, therefore, the ingots need to have larger A.sub.o /A values to achieve comparable strengths to the smaller ingots. Heretofore, however, no method has been known for overcoming this limitation.